Purpose – The goal of this chapter is to explore whether variation in the distribution of union members across the income distribution affects the role of unions in redistributive politics. Design/methodology/approach – The conceptual part of the study provides a theoretical motivation for disaggregating organized labor by income. The empirical part uses European Social Survey data for 15 West European countries 2006–2008 to describe the composition of union membership by income across countries and to explore, in a preliminary fashion, the implications of where union members are located in the income distribution for social protection and redistribution. Findings – In most countries, workers with incomes above the median are better organized than workers below the median and the income of the median union member exceeds the income of the median voter. The political implications of the overrepresentation of relatively well-off workers depend on the mechanism of preference aggregation within unions and the influence of unions in the policymaking process. While leaving a thorough examination of these issues for future research, we present descriptive regression results that indicate that the share of union members below the median does condition the association between aggregate union density and redistribution. It does not condition the association between union density and policy variables that pertain less directly to the distribution of income. Originality/value of paper – This is the first comparative study to map the distribution of union members across the income distribution and to examine the implications of compositional variation by income for redistributive politics.